1. Field of the Invention
The present invention relates to an apparatus for controlling a moving member and others, for example, a control apparatus for an image reader which scans an original, converts the original image into electrical signals by an image sensor and read it.
2. Description of the Prior Art
In the conventional image readers such as copying machines, there is often used a hysteresis or induction motor which is an AC motor. This is because the copying machines require a motor having a sufficiently large torque to read the image of an original and at the same time to drive a photosensitive drum and heat fixation roller used in a process in which the image of the original is transferred to the ordinary paper sheet under the action of charge.
Many AC motors are normally of such a type that is synchronized with an AC frequency used to keep its speed constant. Thus, the synchronized speed can be obtained only at a certain fixed revolution. Even if complicated circuitry is used to change the phase in a drive coil in the range of 2-4 phases, only two synchronized speeds can be obtained. Where the original is copied in reduced and enlarged sizes by using such an AC motor to change the image scanning speed, only two different magnifications can be provided even if the drive phase is changed as described above. If more changes of magnification are required, it is required that a lens system be optically changed in magnification or that the constant revolution of the motor is changed into many desired rotational speeds through a gear box. When it is desired to change the magnification of the lens system, a mechanical construction for positioning the lens system is required, leading to an increase of cost. Further, only a few steps for positioning the lens system can be attained due to mechanical restrictions. The repetitive movement of the lens may result in improper setting positions and images. The gear box may provide only a few steps of change as in the variable power lens system, since the number of gears is geometrically limited. The vibration in the gear box may also contribute to improper images.
There is known a copying machine comprising a fixed platen supporting an original to be copied and a scanner including a source of light for illuminating the original and an optical unit for conducting the light to a photosensitive member. There is also known another copying machine comprising a scanning unit including a movable platen on which an original is placed. Such a scanning unit must be reversed in motion for scanning the image. This requires a reversible motor. Only using such a reversible motor, however, does not enable the direction of scan to be changed because the same motor is also used to drive a photosensitive drum, a fixation section and a system for conveying copy sheets only in one direction. Thus, it has been proposed that the copying machine, have a motor rotable only in one direction, two gear boxes having the respective shafts rotated in different directions and electromagnetic clutches combined with the respective shafts of the gear boxes and used to obtain the desired direction of scan when one of these clutches is engaged. In such an arrangement, means for driving the components other than the scanner is connected with the drive shaft prior to the clutches while the scanner is connected with the drive shaft through the clutches. As a result, the components other than the scanner can be driven always in one direction while the scanner can be changed in its direction of motion. However, the use of two clutches results in various disadvantages, such as increased cost, improper timing due to friction in the clutches, an increased overrun due to the free movement of the final drive shaft during change of one clutch to the other with the resulting increase of scanning period, an improper timing adjustment due to the different frictions in the clutches, and so on.
If more changes of magnification are desired, the number of clutches is correspondingly increased. If the scanner is reciprocated always at the same speed, time is wastefully consumed since the scanner must return to its original position at the same speed as in its forward stroke even when an image is copied in larger sizes. To overcome this problem, a drive system may be further provided to drive the scanner at a higher speed during its return stroke. This leads to an increase of cost. If the clutches are operated over a prolonged period of time, they are degraded, which increases noise and vibrations which will cause improper by formed images.
There has recently been developed a combination of an image reader with a printer in which the image reader is optically separated from, but electrically connected with, the printer. In such a reader, an original is imaged by one on a line sensor of CCD or the like which is one of image pick-up solid state elements, and then scanned in the primary scanning direction to convert the linear image section into signals corresponding to digital values for black and white image portions. Subsequently, the line sensor is moved in the secondary scanning direction for reading the next image line. Since the electrical signals are stored in a memory, the line sensor is no longer required to move in the secondary scanning direction in synchronism with the printer. In this case, a pulse motor is often used which can simply be operated at any synchronized speed in the secondary scanning direction proportional to the number of input pulses. Such a pulse motor is however disadvantageous in that if the rotational speed is increased, the motor does not satisfactorily operate since the starting torque thereof is relatively small in comparison with the geometrical configuration and power consumption of the motor. As a result, the rotation of the motor cannot be increased to any desired speed and/or it may become unstable. Thus, the pulse motor is not suitable for use in the case of driving the line sensor at a higher speed when it is wanted to effect the copying operation at a changed magnification. To satisfactorily actuate the pulse motor causes the efficiency thereof to reduce since a resistor used to drive the motor at lower current consumes more power. In the case that the pulse motor is changed in speed through a gearing, the pulsation of the motor increases noise and vibration. The rotation of the pulse motor does not follow the fluctuation of load to improve the image in accuracy because the pulse motor is only rotated in proportion to the number of input pulses, but not controlled in a closed loop to rotate it in synchronism with the printer.